Organopolysiloxanes with Bunte salt groups linked over carbon atoms have previously been disclosed.
Such organopolysiloxanes are thus taught in German Pat. No. 3,323,881. These organopolysiloxanes with Bunte salt groups correspond to the general formula ##STR1## wherein
R.sup.1 is methyl, with the proviso that up to 10% of the R.sup.1 groups may be alkyl with up to 18 carbon atoms, vinyl, phenyl or hydroxyl groups or hydrogen,
R.sup.2 is ##STR2## wherein one of the R.sup.3 or R.sup.4 groups is a hydroxy group, while the other is --S.sub.2 O.sub.3 Me (Me=alkali metal or an ammonium group which may be optionally substituted), with the proviso that, in up to 50% of the R.sup.2 groups, R.sup.3 and R.sup.4 may be hydroxyl or, together, the oxygen moiety of an oxiran ring,
a has any value from 1 to 2.33 and
b has any value from 0.02 to 1.
Bunte salts are hydrolyzed by aqueous acids with formation of thiols. In alkaline medium, the materials formed include the corresponding disulfides. The reactivity is utilized, for example, to fix dyes with Bunte salt groups to textile material.
The functional groups of the fibers, such as the OH groups of cellulose, the amino and thiol groups of wool or the acid amide groups of synthetic polyamides, react in this dye-fixing reaction as neucleophilic agents. After pretreatment of cellulose with sodium sulfide solution or in the treatment of wool, a polycondensation reaction takes place on the substrate with formation of disulfide bridges. A corresponding dyeing with Bunte salt dyes is therefore waterproof.
The organopolysiloxanes with Bunte salt groups described in the German Pat. No. 3,323,881 are suitable for the surface treatment of inorganic and organic materials. They have been shown to be particularly suitable for the treatment of textile materials, especially wool. It is a particular advantage of these compounds that, when applied on textile surfaces, they are cross linked already at room temperature by the addition of sodium sulfide with the formation of a film, resulting in a permanent finish of the textile material. Fibers and yarns and woven, knitted, nonwoven or other materials can be treated in this manner.
These compounds are particularly suitable for shrink-proofing wool. For this purpose, the compounds are applied on the fibers in the form of a solution or dispersion in water or water/alcohol mixtures in amounts of 0.1 to 5%. The finishes obtained are resistant to organic solvents, such as those used, for example, in dry cleaning.
In contrast to conventional methods for finishing wool, especially for finishing woolen slubbing, the oxidative pretreatment of the fibers can be omitted in this method. This represents distinct progress, since the fibers can be damaged significantly by treatment with chlorine or peroxides.
Aside from the treatment of textiles, the known Bunte salt groups containing siloxanes, can furthermore be used very advantageously for providing other solid materials, such as paper or slag wool with a hydrophobic finish. In these applications also, the important special feature of the siloxanes containing Bunte salt groups lies therein that they can be caused to cross link already at room temperature by the addition of sulfides.
The Bunte salt groups containing siloxanes, described in the German Pat. No. 3,323,881, dissolve in water, provided they contain a sufficiently large proportion of Bunte salt groups. There is a relationship between the number of silicon atoms in the polysiloxane and the number of Bunte salt groups required for solubilization. As the molecular weight of the organopolysiloxane increases, an increasing number of Bunte salt groups is required for water solubility. However, application disadvantages, which arise out of the increase in the cross linking density of the polymer cross linked on the substrate, stand in the way of increasing the number of Bunte salt groups. A highly cross linked polymer can produce an undersirably hard handle in finished fabrics. The increase in the cross linking density leads to an increase in the shrinkage of the polymer that is formed. As a result, the coating of inorganic or organic materials can become uneven or incomplete.
Due to the reaction of the Bunte salt groups, the hydrophilic portion of the organopolysiloxanes is lost during the cross linking reaction and the finish necessarily develops water-repellent properties on the substrate, which are frequently undesirable.